Intermolecular Interactions in Second Harmonic Generation-Active Azobenzene Mixed Monolayers

Mixed self-assembled monolayers (SAMs) are a promising way to tailor surface properties. In this work, we studied the preparation of mixed azobenzene SAMs on silica and the impact of dilution on surface composition, molecular distribution, and interfacial order. Azobenzene-containing SAMs were prepared by postfunctionalization of azide-terminated SAMs through a Huisgen click reaction using solution mixtures of azobenzene (x%) and a diluting agent (1 – x%) at different ratios (x = 0, 10, 25, 50, 75, 90, 100). To rationalize structure–property relationships, three distinct azobenzene derivatives were selected. Successful immobilization was confirmed by PM-IRRAS and ToF-SIMS, and surface density was determined by polarized UV–visible reflection–absorption spectroscopy. Results reveal efficient transfer of the solution ratio to the surface in the high-dilution regime due to the absence of steric hindrance. Combined with polarized second harmonic generation, this approach enabled estimation of the angular orientation probability of azobenzene molecules within the monolayer as a function of dilution. We show that azobenzenes anchored via a flexible linker are influenced by dilution, allowing intermolecular interactions to govern molecular organization. In contrast, rigidly anchored azobenzenes are more constrained, resulting in weaker dependence on dilution and intermolecular interactions.